The present invention relates to methods of making light modulating capacitors and is of particular interest in the provision of a panel comprising an array of display many light modulating capacitor pixels comprising fixed electrodes and movable electrode shutters.
Almost from the dawn of the industrial age, scientists were fascinated with the possibility of communication between remote points in coded, audio and visual formats. In France, even as early as the late 1700""s, elaborate semaphore systems enjoyed substantially widespread use. While such systems achieved their maximum readability during the darkness, and relied, to a large extent, on a subjective evaluation of a signal by the human eye in a sometimes noisy environment, the same represented a dynamic leap of progress over previously employed communications systems.
The invention of the telegraph by Morse in the early 1800""s provided a means for rapid communication which effectively addressed virtually all the perceived limitations of semaphore communication. While the telegraph did require the installation of a telegraph wire hundreds and, ultimately, thousands of miles long, the telegraph insulated its users from dependence on good visibility conditions, fog, rain, atmospheric conditions and high levels of skylight due to natural and/or artificial causes. In addition, being a digital system, it gave users an output that was as sharp, noise-free and readable at the point of reception as it was at the point of transmission.
Even before the invention of the telephone by Bell in 1876, it was recognized that electrical wires could be used to transmit video signals from a transmission point to a remote location. At least as early as the 1860""s, French scientists proposed the possibility of scanning an object illuminated by candlelight using a Nipkow disk, reading the reflected light using a photoelectric device, and transmitting the signal over a wire to a remote point for recording on paper impregnated with gunpowder for viewing.
The weak point in that system (as well as in all modern video systems) was the display. Their proposed solution was to scan a sheet of paper mounted on a drum and impregnated with gunpowder with a high voltage ignition spark which burned in the image scanned by the Nipkow disk. While those familiar only with current state-of-the-art display technology might view such a technique as impractical, it was exactly this display technology which was employed by the great international news services during the first half of the 20th century to transmit photographs by wire. Systems of this sort remained in service at least through the 1960""s.
Although this system had many inherent limitations, it had a number of virtues which no other widely employed display technology has succeeded in matching. For example, the system used very low power and produced very clear sharp images. Unlike liquid crystals, received pictures were visible over a wide angle of view. Unlike cathode ray tube images, images produced by this system enjoyed superb readability even under intense illumination. Still yet another advantage of this system was its low cost.
Of course, such a system could only have limited application because of the exhaustion of the display member by a single frame of transmitted information.
While, during this early period in the history of video display technology, researchers working in the field may have entertained the possibility of a transient reflective mosaic as a video display, a transient controllable light source must have appeared to have a much greater possibility of success, given the number of candidates which included, even at the turn of the century, the incandescent lamp, the neon lamp, and, of course, the cathode ray tube. The earliest commercial xe2x80x9cvideoxe2x80x9d displays were signs, the most notable being so-called xe2x80x9cneonxe2x80x9d signs and incandescent bulb matrix arrays, such as those found on news marquees.
However, with the rapid development of vacuum tube technology in the period surrounding World War I, the cathode ray tube became a practical solution, insofar as it relied upon plate, vacuum and grid technologies, all of which had been developed for other purposes.
Notwithstanding the limitations of the cathode ray tube, which included poor readability in sunlight, cumbersome size, excessively high voltage, the possibility of dangerous X-radiation, and so forth, researchers adopted what must now be considered a low-tech solution and proceeded instead to develop camera technology. Thus, even today, the cathode ray tube in a form substantially unchanged from its earliest embodiments remains the display standard, nearly a century after it was proposed.
When the time came to select a standard format for color television, a purely electronic display system was again selected. While some consideration was given to a rotating color filter wheel system developed by the Columbia Broadcasting System, those responsible for selection of a national color television standard were uncertain whether we would ever have the technology to reliably mechanically control a video display and thus opted in favor of what would also come to be recognized as a problematic approach, namely, the shadow mask cathode ray tube. There was also a general bias against mechanical systems in what was assumed to be the emerging all electronic world.
In one sense the concensus was correct, and the development of better synchronization systems, improved mask configurations and systems, and manufacturing controls resulted in definitively stable and extremely high quality displays. However, nearly a half century later the inherent limitations of the cathode ray tube have also become painfully apparent. So-called xe2x80x9clarge screenxe2x80x9d televisions can only be achieved by using small tubes and clumsy projection optics. Resulting pictures are of such low intensity that acceptable viewing can only be had in the dark. Stray light creates general deterioration in image resolution both by decreasing the signal-to-noise ratio in the display picture and reducing the chrominance content of the projected picture. The end result is a physically large, high voltage and high power system which produces a poor dim picture. Finally, there is a growing concern over CRT radiation output, above and beyond the X-band radiation problem which was substantially solved in the 1970""s. There has never been any significant use of the CRT in outdoor displays, which still use light emitting elements such as the incandescent light bulb and more recently light emitting diodes.
In an attempt to address these problems, manufacturers have turned to liquid crystal display technology. While such display technology may lend itself to moderately large flat displays which will operate at relatively low voltage, such displays are very expensive to manufacture.
A most promising candidate for the solution of the above problems is the (xe2x80x9cLMCxe2x80x9d) or light modulating capacitor. LMC""s come in a wide range of structures and include reflective as well as transmissive devices.
Generally, light modulating capacitors comprise at least one fixed electrode and an active electrode typically made of metalized plastic film. Modulation of light in a pixel is achieved by physical displacement of the active electrode with respect to the fixed electrode, changing the reflective and/or transmissive characteristics of the device. Actuation of the active electrode is accomplished by electrostatically attracting or repelling the variable electrode to a desired position. In the case of an active electrode made of metalized Mylar brand polyester film, the electrode is extremely light, may be prestressed to increase the range of configuration possibilities, and requires extremely low power and relatively low voltage to operate effectively and quickly.
When I first proposed such a device in the early 1970""s, the active electrode generally had the shape of a flapper which was electrostatically driven from one position to another, typically in a two color grove having a V-shaped cross-section, much like a pair of differently colored pages in a half-opened book. Because the flapper is highly reflective, when it is in a first position, it reflects the color of the inside of the groove on the side of the groove opposite that on which it is resting. Thus, when each side of the V-shaped groove is given a different color, the groove appears be to completely the color of the side opposite the active electrode. Because this could be a reflective device, it operated well in ambient light and with only the smallest consumption of electricity insofar as the light modulating capacitor would only pass enough current to charge its internal capacitance.
I have previously proposed the possibility of a prestressed metalized plastic electrode which, in its relaxed state comprised a coiled active electrode which would be electrostatically unrolled over a flat panel, thus changing the color of the flat panel to the color of the active electrode with the device configured as a light reflecting capacitor. Such devices are sometimes referred to as being of the roll-out type. I have also suggested the possibility of a light transmitting window where the device might be backlit and the active electrode used to control the transmission of light through the device.
Similarly, I have proposed the possibility of a large matrix of light modulating capacitors being manufactured in a mass production operation and comprising a single multi-pixel module. In this system, the pixel took the configuration of a V profile flapper-type device.
While the functional characteristics of the above systems have numerous advantages over competing technologies, such as liquid crystal displays, cathode ray tubes and plasma systems, the complexities of achieving economical manufacture pose particular challenges, insofar as each pixel is embodied in a mechanical part that must move quickly and reliably thousands of millions of times. Wrinkles, excess fabrication material, trapped static charges and the like all compromise functionality. At the same time, the system requires substantial bussing to be fabricated at close quarters to moving pixel parts, increasing the likelihood of the introduction of additional defects into the system.
The invention, as claimed, is intended to provide a highly efficient solution to the problem of how to construct a multi-element matrix display. In accordance with the invention, the same is achieved in the context of a light modulating capacitor of the roll-out type.